1. Field of the Invention
This invention relates to a plasma display device, and more particularly to a method of fabricating a dielectric layer for a plasma display device wherein the dielectric layer is formed by depositing dielectric powder on a substrate directly. Also, this invention is directed to a method of fabricating a fluorescent film wherein the fluorescent film is formed by depositing fluorescent powder on a substrate directly.
2. Description of the Related Art
A conventional alternative current system plasma display panel (hereinafter, AC-system PDP) includes a lower glass substrate 10 mounted with an address electrode 12, and an upper glass substrate 20 mounted with a transparent electrode pair 22, as shown in FIG. 1. A lower dielectric thick film 14 with a predetermined thickness for forming a wall charge and a barrier rib 16 for dividing discharge cells are sequentially formed on the lower glass substrate 10 mounted with the address electrode 12. A fluorescent film 18 is coated on the surface of the lower dielectric thick film 14 and the wall surface of the barrier rib 16 into a predetermined thickness. The fluorescent film 18 is radiated by an ultraviolet generated during the plasma discharge to generate a visible light. Meanwhile, an upper dielectric thick film 24 and a protective film 26 are sequentially formed on the bottom surface of the upper glass substrate 20 mounted with the transparent electrode pair 22. The upper dielectric thick film 24 forms a wall charge like the lower dielectric thick film 14, and the protective film 26 protects the upper dielectric thick film 24 from an impact of gas ions during the plasma discharge. Such an AC-system PDP has discharge cells formed by isolating the lower and upper glass substrates 10 and 20 through the barrier rib 16. He+Xe mixture gas or Ne+Xe mixture gas is sealed into the discharge cells.
All the lower and upper dielectric thick films 14 and 24 used in such an AC-system PDP must have a capability of performing a function of anti-diffusion film as well as improving the discharge sustenance and the radiation efficiency. In order to perform a function of anti-diffusion film, all the lower and upper dielectric thick films 14 and 24 must have a high thermal stability, a high calcining temperature and a dense organization. Also, in order to improve the radiation efficiency, that is, in order to improve the brightness, the lower glass substrate 14 must have a high reflective coefficient in such a manner to reflect a visible light back-scattered from the fluorescent film 18 while the upper glass substrate 24 must a high transmissivity in such a manner to transmit visible lights from the fluorescent film 18 as much as possible. Furthermore, in order to improve the discharge sustenance, the lower dielectric thick film 14 must have a low dielectric constant while the upper dielectric thick film 24 must have a high dielectric constant. For instance, it is required that the upper dielectric thick film 24 have a dielectric constant more than "13" and the lower dielectric thick film 14 have a dielectric constant less than "10".
The dielectric thick films 14 and 24 are formed by a process as shown in FIG. 2. In step 30, non-crystallized glass powder is prepared. In order to prepare the non-crystallized glass powder, raw materials of a SiO.sub.2 --ZnO--B.sub.2 O.sub.3 group non-crystallized glass or a P.sub.2 O.sub.5 --ZnO--BaO group non-crystallized glass are mixed at a desired component ratio. The raw materials of the mixed SiO.sub.2 --ZnO--B.sub.2 O.sub.3 group non-crystallized glass or a P.sub.2 O.sub.5 --ZnO--BaO group non-crystallized glass are heated for about 5 hours into a temperature of about 1100.degree. C. at a melting furnace to be melted. In the period of melting the raw materials of the non-crystallized glass, the raw materials is stirred two or three times to produce a uniform liquid-state non-crystallized glass. The liquid-state non-crystallized glass is suddenly cooled to thereby have a dense organization and to produce glass cullets with minute cracks. The cullets are milled for a desired time (e.g., 16 hours) by the ball milling technique and thereafter passes through #170 and #270 sievers sequentially, thereby making non-crystallized powder having a particle size of about 6 .mu.m. In step 32, such non-crystallized glass powder is mixed with filler powder at a predetermined component ratio. The non-crystallized glass powder and the filler powder having the predetermined component ratio is mixed during a desired time (e.g., 10 hours) by means of a tumbling mixer. In step 34, the non-crystallized glass powder and the filler powder mixed in this manner is mixed with an organic vehicle at a predetermined component ratio to thereby produce a paste. Herein, a mixture of butyl-carbitol-acetate(ICA), butyl-carbitol(BC) and ethyl-cellulose(EC) with the organic vehicle at a desired ratio is used as the organic vehicle. A viscosity of the paste is varied in accordance with a quantity of EC to have an influence on the rheology and sintering characteristic. Subsequently, in step 36, the paste is coated on the glass substrate 10 or 20 at a uniform thickness. The coating of the paste is carried out by a repetitive screen printing. In the screen printing technique, as shown in FIG. 3A, a screen 40 is installed at the upper portion of the glass substrate 10 or 20, and a paste 42 is disposed on one edge of the screen 40. The paste 42 is pushed into other edge of the screen 40 in such a manner to be coated on the glass substrate 10 or 20 at a constant thickness as shown in FIG. 3B. Then, the paste 42 is again put on one edge of the screen 40 as shown in FIG. 3C. The paste 42 is further pushed into other edge of the screen 40 by a squeezer such that it is again coated on the glass substrate 10 or 20 as shown in FIG. 3D. By such a repetitive screen printing, the paste 42 is coated on the glass substrate 10 or 20 at a desired thickness (e.g., 15 to 20 .mu.m). The glass substrate 10 or 20 coated with the paste 42 in this manner is dried during a desired time (e.g., about 20 to 30 minutes) at a temperature of 350 to 400.degree. C. within a dry oven (not shown) at the atmosphere. At this time, an organic vehicle included in the paste is completely burned out. After the organic vehicle is completely eliminated, the glass substrate 10 or 20 is heated into the crystallization temperature during a desired time to sinter a non-crystallized glass included in the paste 42. Consequently, the glass substrate 10 or 20 is cooled during a desired time(e.g., about 40 minutes) at a cooling time of 6.degree. C./min to form a dielectric thick film 14 or 24 on the glass substrate 10 or 20. Herein, the paste 42, that is, a sintering temperature of the dielectric thick film 14 or 24 is set to less than 600.degree. C. so as to minimize a thermal deformation of the glass substrate, 10 or 20.
Such a screen printing technique complicates a dielectric thick film fabricating method because it needs a forming process and a sintering process of the paste. The calcining temperature is too low at the time of sintering the paste, the dielectric thick film is not eliminated completely to have a non-uniform surface. Due to this, the dielectric thick film absorbs or scatters a visible light to have a low light transmissivity. On the contrary, when the calcining temperature is too high, the surface of the dielectric thick film is damaged. As a result, a bonding between the dielectric thick film and the protective film is not only weakened, but also a characteristic of the protective film is deteriorated. The fluorescent film included in the PDP along with the dielectric thick film also is formed by the paste producing process, the screen printing process and the sintering process in similarity to the dielectric thick film. Due to this, the fluorescent film fabricating method also is complicated like the dielectric thick film fabricating method. Furthermore, the fluorescent thick film also has a non-uniform surface because an air gap is not eliminated completely.